Observations on the primordial germ cells of bandicoots (Peramelidae, Marsupialia).

Characteristically, bandicoot primordial germ cells are large, lightly staining cells with vesicular nuclei in which the chromatin is clumped beneath the nuclear envelope. Rounded, lightly staining cells in the yolk sac wall of 9 1/2 days old embryos are tentatively identified as primordial germ cells; as they lack other primordial germ cell attributes it is suggested that they may be prospective primordial germ cells in the process of differentiation. The primordial germ cells reach the prominent gonadal rudiments by migration through the hindgut and dorsal mesentery, as in eutherian mammals. In 9 1/2 days old embryos the primordial germ cells are found in the hindgut endoderm and mesoderm. By day 11 they are migrating in the dorsal mesentery. During migration the primordial germ cells undergo both division and attrition. Primordial germ cells reach the gonadal ridges around the perinatal period. No sexual differences are evident at this stage. As the gonadal ridges develop before the primordial germ cells reach their vicinity their development is clearly independent of the primordial germ cells.